In conventional short-hole drilling, at least two operations are required to form a hole with a strict tolerance. First, a typical drill bit is used to drill a hole having a diameter slightly smaller than the desired diameter of the final hole. Thereafter, a single or multi-point reamer is used to ream the drilled hole, increasing the diameter slightly, and making the final hole the desired size.
In addition to the expense associated with performing multiple operations for each hole, existing short-hole drilling techniques have other problems. In particular, sometimes it is desirable to drill a hole in a workpiece, where the hole being drilled will intersect a blind bore that is already formed in the workpiece. It is rather difficult to drill a hole that intersects an existing blind bore with existing short-hole drilling techniques.
With existing techniques, as a point on the reamer cuts the workpiece during reaming, normal and tangential cutting forces at the point cause the bit to bend slightly. When the point of the tool reaches the intersection of the blind bore with the hole being drilled, the drill bit reacts to the sudden reduction in cutting forces at the point, causing the point to extend slightly into the blind bore. When the point is about to rotate out of the blind bore region, the point may nick the workpiece where the hole being drilled meets the blind bore, and after a while, cause the hole being drilled to be out of specification.
Thus, in short-hole drilling, it is difficult to consistently drill straight holes that meet strict tolerances. Deep-hole drilling techniques have addressed similar problems related to centering a deep-hole drill bit. For example, a gun drill has a bit designed to center itself during drilling. However, there are several things about deep-hole drilling techniques that prevent the easy adaption of deep-hole drilling techniques to short-hole drilling. For example, a gun drill has a bit connected to a long steel shank that is brazed to the bit. The long steel shank bends very easily. As such, although a gun drill may do a good job of drilling a deep hole, a gun drill cannot do a very good job of reaming a deep hole because the long steel shank tends to flex during drilling. If the rough drilled hole that is to be reamed is not straight, the gun drill will simply follow the path of the pre-drilled hole. Thus, the gun drill will not self-center to form a clean bore meeting a strict tolerance.
For the foregoing reasons, there is a need for a short-hole drill bit and short-hole drilling method that overcomes the problems and limitations of the prior art.